1. Field of the Invention
The present invention generally relates to a method for forming an oxide film of a metal or silicon by plasma-assisted processing such as plasma-enhanced atomic layer deposition (PEALD).
2. Description of the Related Art
In a PEALD process, depending on the type of application, there are problems to be solved, such as oxidation of an underlying layer and auto-doping in a process of boron-silicate glass (BSG)/phosphor-silicate glass (PSG). Conventionally, these problems have been handled by lowering RF power.
For example, low RF power is required in the BSG/PSG process for solid state diffusion (SSD) because, as illustrated in FIG. 1a when high RF power is applied, penetration of dopant (boron) 2 into a Si substrate 3 occurs during deposition of a BSG film 1 due to the ion bombardment effect. That is, although a portion of BSG/PSG film is removed from an area where diffusion of dopant is not desired during and after a deposition step, and then heat treatment of the substrate is conducted so that the diffusion of impurities can be confined only to a certain area in the substrate, the unwanted diffusion of impurities will result in another area of the substrate if the diffusion occurs during deposition when high RF power is applied.
Further, low RF power is required in a SiO process where oxidation of an underlying layer 7 is undesired because, as illustrated in FIG. 1b when high RF power is applied, the underlying layer 7 is oxidized due to the effects of oxygen plasma, ion bombardment, and sputtering during film deposition. That is, when a SiO film 5 is deposited by PEALD on the underlying layer 7 in which W, TiN, or other materials are contained or which is a SiN film, the material constituting the underlying layer 7 is oxidized in an upper portion 6 thereof by a plasma including oxidizing gas used for deposition of the SiO film 5, and thereby desired device characteristics cannot be obtained.
In addition, low RF power is required in a process of film deposition on a photoresist because, as illustrated in FIG. 1c when high RF power is applied during the film deposition process, the photoresist dimensions are set back and reduced due to the effects of oxygen plasma, ion bombardment, and sputtering. That is, when an oxide 9 is deposited by PEALD on a patterned photoresist 10 formed on a substrate 11 in a double patterning process, a portion 12 of the underlying photoresist 10 is oxidized and eroded by a plasma including oxidizing gas used for deposition of the SiO film 9, and the desired dimensions of the photoresist 10 cannot be obtained.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.